In bus-oriented communications networks that are used, for example, in automation systems, it is often necessary to remove or add subscribing communications entities without affecting the remaining communications entities during a running communications operation, which is designated by the term “hot swapping.”
For this purpose, for example, field bus systems such as the Profibus or the CAN bus (CAN: Controller Area Network) can be used according to a multi-drop bus system or a multi-drop bus arrangement or topology that is configured, for example, according to the RS 485 standard. Here, the communications bus users are connected in parallel by means of a common communications line, e.g., by means of stub lines or node branches coupled in series with this communications line for the individual bus users. Other field bus systems such as, for example, the SERCOS bus system, are based on a point-to-point system or a point-to-point bus arrangement with interconnected point-to-point connections arranged in the form of a ring. For realizing the redundancy property, here a second ring is often provided, so that a double ring must be realized.
However, both bus arrangements or bus systems have disadvantages. For example, the performance of the multi-drop communications buses is greatly limited by inadequate performance-matching possibilities of the communications network. In addition, in the case of a multi-drop communications connection, selective bus user addressing is required in which each bus user performed an address setting. On the other hand, in the case of an additional design in the form of the already mentioned double ring, a concatenation of point-to-point connections can often compensate only a single interruption in the communications connection. In addition, the known communications bus concepts are not flexible, because each structure does not take into consideration different operating modes of the communications system that could be, for example, data-specific or service-specific.
The problem, therefore, is to create an efficient and flexible concept for bus-oriented communications.